Orthopedic hardware that is inserted in an intramedullary manner has become an increasingly useful aid in treating complex fractures of long bones, e.g., of the femur or the tibia. In a typical application, an interlocking rod or bar, commonly referred to as a "nail," is inserted into a femur and transverse screws or pins, which are screwed or otherwise inserted from the outside of the limb or other body part through the bone and into distal and proximal transverse screw holes in the rod, are used to fix the rod in place in the bone.
The use of such locking screws to ensure that the rod is fixed firmly in position has extended the range of application of such orthopedic aids and appliances well beyond than that of the original locking rods without such transverse screws. However, the problem of properly inserting the screws from the outside of the limb is a difficult one and a number of different approaches have been taken in attempt to find a safe, effective and rapid way of inserting the locking screws and, in particular, the distal locking screws. In this regard, it is noted that such locking rods are long enough that the rods will bend when installed and thus locking or positioning devices which are centered based on a reference taken from the top of the rod have been ineffective in precisely locating the transverse screw holes. It will be understood that the locking screws or pins must be precisely located so that the load on the limb or other part of the body involved is transmitted through the screws or pins and associated interlocking rod and not through the broken portions of the bone during healing.
One method that is capable of providing precise locating of the holes distally uses x-ray techniques but long periods of x-ray exposure are required and the need to move the x-ray equipment in and out of position to check the screw or pin locations means that there is a risk of a loss of alignment each time the equipment is moved. As a consequence, the positioning of such locking screws or pins is typically the most time consuming and difficult portion of the overall rod implantation procedure.
Patents of interest in this field include Brudermann U.S. Pat. No. 4,621,628; Olerud et. al. U.S. Pat. No. 4,625,718, and Wu U.S. Pat. No. 4,570,624. The Brudermann patent discloses an apparatus for locating transverse holes in intramedullary implants and, in particular, transverse holes in the distal end of implanted locking "nails". The apparatus includes at least one magnet which generates an axially symmetrical field in combination with a magnetic field detecting device or sensor having an axial field reception characteristic. In one embodiment, the magnetic field sensor is inserted into an implanted nail and the magnet, which is placed on the surface of the skin, is moved until axes of the magnetic field of the magnet and the sensor are aligned. More particularly, the sensor is connected to an external display device and alignment of the respective magnetic fields is indicated when a zero-point indication is provided on the display device. A second magnet can be used to increase the precision of the alignment process.
The other two patents are thought to be of more general interest, with the Olerud et al patent disclosing an aiming apparatus using X-ray techniques for making holes or bores in the bone of patient in registration with the holes or bores on an interlocking nail, and the Wu patent disclosing a mechanical technique for aligning surgical pins in parallel.